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Biomedical subjects

C E Webber

Publications and source records attributed to C E Webber.

At least 55 records · Page 3Linked to original sources
PubMed1994

Effects of 2 years of hormone replacement upon bone mass, serum lipids and lipoproteins.

The objective of this study was to measure the effects on postmenopausal women of 2 years of either a low dose or a moderate dose regimen of hormone replacement upon bone mass and serum cardiovascular risk factors. After 6 months of calcium supplementation, 75 women chose to add hormone replacement or to remain on calcium. Those choosing hormones were randomised to either 0.3 mg/day equine estrogen and 2.5 mg/day medroxyprogesterone or 0.625 mg/day equine estrogen, days 1-25, and 5 mg/day medroxyprogesterone, days 16-25. On calcium only, lumbar spine bone mineral content and radius bone mass fell. Serum concentrations of cholesterol and triglycerides increased while HDL concentration fell. The low dose continuous regime reduced whole body bone turnover and prevented the age related reductions in bone mass and serum cardiovascular risk profile. The moderate dose regimen reduced whole body bone turnover and increased lumbar spine bone mass. Total serum cholesterol was unchanged while HDL levels increased, LDL levels fell and triglyceride concentration increased.

Adult↗
PubMed1994

Measurement of the natural uranium content of fabricated, tissue substitute lung sets by dual photon absorptiometry.

The assessment of tissue substitute materials by dual photon absorptiometry has been extended to detect the presence of high atomic weight materials. Commercial dual photon systems dedicated to the measurement of bone mineral mass can be used to detect other elements in fabricated tissue phantoms. The technique is sufficiently sensitive to quantitate the mass of natural uranium that had been distributed throughout the lungs of a thorax phantom.

Absorptiometry, Photon↗
PubMed1994

In vivo measurements of bone lead content in residents of southern Ontario.

In 111 subjects not occupationally exposed, bone lead content increased steadily with age in both men and women. Higher than expected bone lead levels were observed in two-thirds of 27 subjects working in occupations with potential for lead exposure. Five of 8 patients who displayed symptoms which might have been due to lead poisoning had increased bone lead levels. In vivo bone lead measurements reflect the cumulative extent of exposure to environmental and occupational sources of lead and allow the assessment of abnormal exposures.

Adult↗
PubMed1994

Comparison of whole and split weight training routines in young women.

Thirty young women comprised three groups (n = 10 in each): whole routine (W) training, split routine training (S), and control. The W group did four upper (five sets, 6-10 RM) and three lower body (five sets, 10-12 RM) weight training exercises together in single sessions twice a week for 20 weeks. The S group did the upper body exercises 2 days a week and the lower body exercises on 2 other days of the week. The single maximal weight lift (1-RM) increased (p < 0.05) (W/S) 54/69%, 33/32%, and 21/22% in arm curl, bench press, and leg press exercises, as did arm (10/9%), and trunk (3.4/2.7%) lean tissue mass, as measured by dual energy x-ray absorptiometry. Leg lean mass increased significantly only in W (4.9% vs. 1.7% in S). Whole-body lean tissue mass increased (4.1/2.6%), and whole body % fat (-1.1/-1.3%) decreased with training. It is concluded that in healthy young women, whole and split weight training routines produce similar results over the first 5 months of training.

Adult↗
PubMed1994

The reproducibility of 109Cd-based X-ray fluorescence measurements of bone lead.

We assessed the reproducibility of X-ray fluorescence-based lead measurements from multiple measurements made on a low-concentration plaster of paris phantom and in five subjects measured five times on two occasions. Over a 6-month period, 220 measurements of the same phantom were obtained and showed a standard deviation of 1.29 micrograms Pb (g plaster of paris)-1. The two sets of in vivo measurements were made 10 months apart and revealed a mean standard deviation of 3.4 micrograms Pb (g bone mineral)-1 and 5.1 micrograms Pb (g bone mineral)-1 for males and females, respectively. Our measured standard deviation exceeded by 20-30% the calculated standard deviation associated with a single measurement both in the phantom and in subjects. This indicates that some variance is introduced during the measurement process. Operator learning and consistency significantly minimized this increased variability. Measured lead concentrations of the left and right tibia in 14 subjects showed no significant differences between legs. As a result, either tibia can be sampled and compared over time. The levels of reproducibility we report here mean that X-ray fluorescence-based determinations of bone lead concentrations are reliable both over the short and long term. Thus, reasonably sized confidence intervals can be placed on detected changes in concentration and should permit acquisition of longitudinal data within a reasonable length of time.

Bone and Bones↗
PubMed1993

A multi-element isotopic tracer assessment of true fractional absorption of minerals from formula with additives of calcium, phosphorus, zinc, copper and iron in young piglets.

True fractional absorption of minerals was measured to determine the bioavailability of Zn, Fe, Mn and Se from liquid formulas fortified with stepwise additions of Ca and P (as Ca glycerophosphate and carbonate, Ca*P), and Zn, Cu and Fe (as sulfate salts). Growth, deposition of tracers in organs and bone mineral content of femurs as assessed by single photon absorptiometry were measured. Four-day-old piglets (n = 36) were randomly assigned to groups fed a basal diet or additions of Ca*P (Ca = 25, P = 18 g/kg dry diet), Ca*P+Zn (Zn = 0.04 g/kg), Ca*P+Zn+Cu (Cu = 0.007 g/kg) or Ca*P+Zn+Cu+Fe (Fe = 0.008 g/kg). Oral and intravenous administration of extrinsic isotopes of 59Fe, 54Mn, 65Zn, 75Se and 47Ca was followed by fecal monitoring for 15 d and true absorption calculated after accounting for endogenous excretion. Addition of Ca*P+Zn reduced Zn absorption (P < 0.05) and Ca*P+Zn+Cu reduced Fe absorption (P < 0.01), but Mn and Se absorptions were not altered. Uptake of only Zn tracer into heart was significantly different (P < 0.05) among diet groups. Weight gain and linear growth were similar in all groups. Addition of Ca*P produced higher bone mineral density, but its effect on Zn absorption warrants further investigation.

Absorptiometry, Photon↗
PubMed1993

An improved instrument for the in vivo detection of lead in bone.

An improved instrument for the fluorescence excitation measurement of concentrations of lead in bone has been developed. This is based on a large area high purity germanium detector and a point source of 109Cd. The source is positioned in a tungsten shield at the centre of the detector face such that 88keV photons cannot enter the detector directly. In vivo measurements are calibrated with plaster of Paris phantoms. Occupationally non-exposed men show a minimum detectable concentration of about 6 micrograms/g bone mineral. Measurements of tibia lead concentrations in 30 non-occupationally exposed men between the ages of 23 and 73 showed an annual increment of 0.46 microgram/g bone mineral/year. The mean deviation from the regression of tibia lead upon age was 3.5 micrograms/g bone mineral. Tibia lead concentration in one subject with a history of exposure to lead was 69.6 (SD 3.5) micrograms/g bone mineral. The improved precision of the point source large detector system means that greater confidence can be placed on the results of in vivo measurements of lead concentration. This will allow studies of the natural history of non-occupational lead accumulation in normal subjects and should permit investigations of the efficacy of therapeutic interventions in subjects poisoned with lead.

Adult↗
PubMed1993

Correlates and determinants of bone mineral content and density in healthy adolescent girls.

The relationships between whole-body and lumbar spine bone mineral content and density, and measures of chronologic age, body composition, physical activity, cardiorespiratory and strength fitness, gynecologic attributes, sexual maturity, and endocrine status were studied in 35 healthy menarcheal girls (14-18 years of age). Body mass (0.464 < r < 0.704), growth hormone (-0.34 < r < -0.42), and one-repetition maximum double-leg press strength (0.343 < r < 0.467) were significantly (p < 0.05) correlated with each of the five bone mineral measures. Multiple regression analysis indicated that body mass accounted for the largest significant proportion of the explained variance (30.2-68.2%) in each of the five bone mineral measures. Age at first menses accounted for a smaller but still significant proportion of the variance in whole-body bone mineral content (4.05%) and lumbar spine bone mineral content (8.06%). Growth hormone entered the regression model as an important predictor of whole-body bone mineral content, accounting for 3.51% of the explained variance in this variable. Age, cardiorespiratory fitness, level of habitual activity, and strength did not contribute significantly to the explained variance in any of the bone mineral measures. Body mass appears to be the single most important determinant of bone mineral among females during this developmental period.

Adolescent↗
PubMed1993

Comparison of three techniques for body composition analysis in cystic fibrosis.

Body composition analysis is an important component of nutritional assessment in cystic fibrosis (CF). No gold standard of measurement exists, and techniques applicable to healthy populations may be unsuitable for CF patients. We assessed lean body mass (LBM) in 12 children with CF by skinfold (SK) measurements, bioelectrical impedance analysis (BIA), and dual-photon absorptiometry (DPA) and repeated these measures in 10 subjects 6 mo later. SK and DPA measures in eight older CF patients and eight healthy controls were compared to evaluate any effect of disease on estimates of LBM by use of DPA. Good agreement between the measures was seen at baseline and 6 mo by use of concordance plots. However, the limits of agreement between measures ranged up to 19% of SK-derived LBM measures (baseline: SK and DPA, 2.63 to -3.93 kg; SK and BIA, 2.36 to -1.24 kg; BIA and DPA, 1.88 to -4.28 kg; 6 mo: SK and DPA, 2.10 to -3.58 kg; SK and BIA, 6.28 to -5.49 kg; BIA and DPA, 5.53 to -7.79 kg). The change in LBM over 6 mo did not correlate among the three measures. Only BIA change in LBM correlated with weight change (r = 0.716, P < 0.02), probably due to the inclusion of weight in the regression equations for determining LBM from impedance. The relationship between SK and DPA measures did not differ between the CF and control groups, suggesting that there was no effect of disease on the DPA measure. The results suggest that none of these methods is precise enough to follow short-term changes in the nutritional status of CF patients longitudinally.

Absorptiometry, Photon↗
PubMed1993

Body composition and bone mineral distribution during growth in females.

The total mass of lean tissue, fat and bone mineral was measured in a cross-sectional study by dual-photon absorptiometry in 76 normal, ambulatory females aged 8 to 26 years. These measurements allowed quantification of average total-body bone mineral density and assessment of the mass and the average density of bone mineral in different regions of the body, specifically the head and the legs. Both total-body and regional results are presented as logistic functions of age; the functions were derived by nonlinear regression analysis. Normal ranges, defined as twice the root mean square deviation about the fitted equation, are also expressed as functions of age. As well as providing normal reference values, these data suggest that muscle mass is an important determinant of total-body bone mineral mass and that peak bone mass is achieved at different ages in different regions of the skeleton.

Absorptiometry, Photon↗
PubMed1992

Evaluation of the Lawrence Livermore National Laboratory (LLNL) torso phantom by bone densitometry and x-ray.

The recent Workshop on Standard Phantoms recommended that the LLNL torso phantom be adopted as a calibration standard for the quantitation of in vivo radioactivity. This phantom was designed for the calibration of systems for the detection of x-rays of less than 20 keV. The anthropomorphic characteristics and tissue substitute composition of the phantom were assessed with techniques using photons of higher energy. Dual photon absorptometry at 42 and 100 keV showed that the phantom was representative of in vivo tissue composition. Chest radiography showed that the phantom was representative of a human even though the stomach, GI tract and the scapulae were not present and air gaps were observed at organ boundaries.

Absorptiometry, Photon↗
PubMed1992

Relationship among running mileage, bone density, and serum testosterone in male runners.

Our purpose was to investigate the relationship between running volume and bone mineral mass in adult male runners. Whole body and regional bone mineral density were determined by dual-photon absorptiometry in 22 sedentary controls and 53 runners who were selected according to their running mileage to fall into a 5- to 10-, 15- to 20-, 25- to 30-, 40- to 55-, or 60- to 75-mile/wk group. All groups were of similar age (20-45 yr) and nutritional status, as determined by 7-day food records. Regional sites for bone density measurements included the trunk, spine, pelvis, thighs, and lower legs. In addition, serum total testosterone was determined in each subject and computed tomography scans were made of the lower legs in 34 subjects to assess bone cross-sectional area. No significant differences were detected for bone density measurements with the exception of the lower legs where it was significantly (P less than 0.05) greater for the 15- to 20-mile/wk group than for the control and 5- to 10-mile/wk groups. With mileage greater than 20 miles/wk, bone density of the lower legs showed no further increase and, in fact, tended to decrease, so that for the 60- to 75-mile/wk group it was similar to that of the controls. Cross-sectional area of the tibia and fibula when normalized to body weight tended to be greater as weekly mileage increased and was significantly greater in the 40- to 55-mile/wk runners than in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Phantom studies of triple photon absorptiometry and bone mineral measurement at a hip prosthesis.

The feasibility of using triple photon absorptiometry (TPA) for the measurement of bone mineral mass about a hip prosthesis was examined. A theoretical expression describing the variance of TPA measurements was verified using a triple photon source and phantom materials which simulate the soft tissue-bone mineral-metal prosthesis system. The expression for the variance was used to determine an optimized set of photon energies. It was shown that a precision of 3% could be obtained for reasonable measurement times using this optimized set of energies, and that TPA should be a feasible approach for measurement of bone mineral about a hip prosthesis.

Absorptiometry, Photon↗